Buck is pretty much right, the cosmetics are the real difference. I have handled both (and own 7 GW's myown self)
But ifn you want some real buttkickin smooth shooter, The Alchemista beats all of them (and most other brands hands down)
Old Top had been houndin them to get him some 1860 grips for his gw's because they fit bigger hands better. Well that is exactly what Alchemista did. He fitted the 60 grips to the Great Western, and then put a wider trigger CENTERED in the frame, and the action job is outstanding....it is well smooth as glass...I can't even describe it.
But back to your question, basicly they are the same, the finish is the real difference, but what a difference...The Turnbull finish is beautiful and the custom nickel is awesome..